VIII. 



THE SPERMAPHYTES. 



The eighth subdivision includes the higher and so- 

 called Flowering Plants. They vary in size from plants 

 a small fraction of an inch in height up to the mightiest 

 trees. They are, in general, plants of a highly differen- 

 tiated and complex structure. The plant is the sporo- 

 phyte. There are two kinds of spores, microspores or 

 pollen grains, and macrospores borne in embryo sacs. 

 The contents of the pollen grain develop by cell division- 

 into a minute prothallium which takes the form of a tube 

 projecting from the pollen cell. The contents of the 

 embryo sac also develop into a minute prothallium. 

 These prothallia represent the gametophyte. The first 

 step in the reproduction is the extension of the pollen 

 tube, which is an outgrowth of the inner coating of the 

 pollen grains, into the embryo sac, contact with the viscid 

 secretion of the stigma being a necessary prerequisite to 

 the growth of the pollen tube. As the pollen grains are 

 not self -motile, nature provides for their transportation 

 from the anther to the stigma, by means of the wind, by 

 the adaptation of the various parts of the flowers to this 

 end, and by rendering the flowers attractive to various 

 insects, either because of the nectar which furnishes food 

 for the insects or because of their colors which attract or 

 serve as a means for concealment or protection for them. 

 These little creatures carry the pollen from anther to 

 stigma on the same or on different flowers. 



The feature that especially distinguishes the Sperma- 

 phytes from the plants of the seven preceding subdivi- 



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